The present invention relates to thrust rings for pipe joints. The term the "thrust ring for pipe joints" refers to a washerlike ring which is interposed between a joint member of a pipe joint and a connecting threaded member, such as a hollow bolt or cap nut, rotatably fitted to the joint member for preventing the joint member and the threaded member from rotating together.
Pipe joints are known which comprise a pair of joint members each having an outer flange at one end, an annular gasket interposed between the flanged ends of the joint members, a hollow bolt having an externally threaded surface and a bore extending axially therethrough for inserting one of the joint members through the bolt, and a cap nut having an internally threaded surface screwed on the externally threaded surface of the hollow bolt and formed with a hole in the center of its top wall for inserting the other joint member therethrough. A thrust ring is interposed between the flange of one of the joint members and the inner end of the hollow bolt, as well as between the flange of the other joint member and the inner surface of the top wall of the cap nut. The conventional thrust rings for use in such pipe joints are in the form of an endless ring.
Since the conventional thrust ring is endless and annular, it is impossible to fit the ring to the joint member or to remove the ring therefrom by moving the ring in a direction perpendicular to the axis of the joint member. Further because the inside diameter of the thrust ring is of course smaller than the outside diameter of the flange of the joint member, the ring can not be attached to or removed from the joint member from the flanged end thereof. In other words, the thrust ring can be attached to and removed from the joint member only from one end thereof opposite to its flanged end. For this reason, two pipes are joined together by the pipe joint, for example, by fitting the thrust ring and the threaded member (hollow bolt or cap nut) to each joint member from one end thereof opposite to the flanged end before the pipes are connected to the respective joint members, then fitting the end of each pipe to be joined to the end of the joint member opposite to the flanged end, welding each of the fitted joints thus formed, and fastening the two threaded members to each other with a gasket interposed between the ends of the joint members to connect the joint members together.
The thrust ring for use in pipe joints is likely to corrode or become damaged or broken during use by being exposed to a corrosive liquid or gas, so that there arises a need for replacement. Further it is likely that a pipe will be connected to the pipe joint inadvertently without incorporating the thrust ring into the joint. The thrust ring must then be installed after connection.
Nevertheless, the conventional thrust ring can not be removed from or attached to the joint member except from the end thereof opposite to the flanged end as described above, so that the thrust ring can not be replaced or attached after the joint member has been welded to the pipe even if the two threaded members are separated to disassemble the pipe joint. Accordingly, when the thrust ring only is to be replaced, the ring is replaced, for example, by separating the two threaded members to disassemble the pipe joint, cutting the pipe having the old thrust ring at a suitable portion, removing the threaded member and the old thrust ring from the cut end, attaching a new thrust ring and the threaded member to the joint member, welding the cut portion of the pipe and thereafter fastening the two threaded members to each other to connect the joint members together. However, the procedure for replacing the thrust ring is very cumbersome and takes time. This is also true of the thrust ring which needs to be installed after connection. It is also likely that the piping including the pipe joint and the pipes on opposite sides thereof will be wholly replaced by a new piping system when there arises a need to replace or install the thrust ring after connection, whereas this is uneconomical.